High frequency telephony system



June 9. 1931- I P11-ATZ Y 1,809,081]

HIGH FREQUENCY TELEPHONY SYSTEU Filed June 13., 1925 f Paws MRR/E@ souk" WAVE SOURCE 2J) CARR/e@ I WA VE POM/ER Jou/PCE SOURCE 2J i F195 i294 y my; 6"

mm- L f 36 J/ www ig. .746, 59.4% i @im Patented June 9, 1931 UNTED STATES PATENT ori-ic PAUL TTZ, OF BER-LIN, GERMANY, ASSIG'NOR T0 GESELLSCHAFT FR DRAHTLOSE TELEGRAPHIE M. B. E. HALLESCHES UFER 112./13, BERLIN, S. W. 11, GERMANY, A

CORPORATION 0F HIGH. FREQUENCY TELEPHONY SYSTEM Application led June 12, 1925, Serial No. 36,670, and in` Germany June 13, 1924.

This application relates to a method and means for avoiding disturbances in wired wireless telephony on high tension powerk transmission lines caused by changes in con nection of the power apparatus.

Radio frequency telephony over high tension transmission lines encounters many difiiculties in practice which are based upon the fact that transmission lines are primarily devoted to long distance transmission of electrical power, and only secondarily to transmission of intelligence. Therefore, it is absolutely necessary that radio frequency telephony over power transmission lines be subordinated to the eXigencies of high tension power service. It is very often quite difficult to solve the problems encountered in this respect.

The high tension power transmission service-often causes alterations of the state of the ends of the transmission lines. In normal condition these lines are connected to the main cholres of the central stations or switch plants which serve to distribute the energy. Tf the supply of energy is stopped, the ends of the transmission lines are either left free cr are connected to earth. When working on the transmission lines for repair or maintenance purposes, both ends of these lines must be connected to earth for the protection of the working stad. There are still more possibilities for the state of the ends of the lines, for example, transmission lines of larger stations are sometimes used for transferring currents of dierent frequencies or voltages, and are connected to various supply systems according to need. Thesey different systems of supply, distribution or consumption may, of course, differ greatly and materially. Y

At is clear that for purposes of radio frequency telephony over power transmission wires, these frequent alterations of the state or condition of the ends of the lines must be taken into consideration. From this it follows, of course, that it is necessary in practice to arrange the connection point, (in a general sense) of the telephony apparatus before the switches of the transmission lines `alone could not suflice.

at their starting point, and not inside the central station or switch plant.

Considering that an undisturbed service of the telephony system always requires a certain constant voltage of the telephony carrier frequency at the ends of the transmission lines, this method of connection The central stations or switch stations, however, represent for the greater part a very undesired load, acting parallel to the transmission lines for the carrier frequency. It is obvions that the unavoidable alterations of this parallel load ing, or in other words, of the alteration of the state of the ends of transmission lines must influence the distribution of voltage of the carrier frequency at the ends of the line in a very undesired manner. y

The diiiiculties caused hereby may be eX- plained by an example. The carrier frequency is often transferred to the transmission lines by means of high tension condensers. This kind of coupling, capacitive coupling, acts in such a way that a certain voltage of the carrier frequency is produced at the connection point of the condenser, and heterodyned upon the useful low frequency and spread over the lines. The system of the main bus-bars of ihe central station, to gether with the transformers, voltage, converters, etc., have, according to their size, a high, or low, apparent impedance for the carrier frequency, and when the transmission lines are connected up, this apparent impedance is put in shunt with the lines.

If the apparent impedance of the central station is low, which is usually the case, this shunt 'causes great losses of the carrier frequency, and it is difficult to attain the initial impressed voltage which is necessary for good communication, on the transmission line. If the transmission lines are disconnected from the main bus-bars, the high parallel loading does not take place, the initial voltage of the lines is greatly altered, and the telephonie connection disturbed. Tf the transmission lines are earthed at the central station, the initial voltage decreases to 'zero because of the short circuit and the telephonie connection fails complet-361? Various remedies have in the past been employed to overcome the above-mentioned difficulties caused by the alterations of the state of the ends of the transmission lines, resulting in undesired loading of the carrier frequency by the central station, which load is not present upon opening' the circuit or disconnecting the transmission lines from the station. However, the load is a direct short circuit whenever the lines are earthed at the station.

One such remedy was to utilize great power and large transmitting outputs in order to maintain telephonie connection during unfavorable times when the connection relations were poor. In order to avoid a short Circuit caused by the connection to earth, choke coils for the carrier frequency were inserted in the connections to earth.

However, this measure caused an undesired radiation into space and furthermore, the output of the transmitter was uneconomically enlarged during the time when favorable connections were established. Therefore, the value of the communications was subject to great fluctuations independent and apart from the diHiculties of calling, which are caused by great fluctuating receiving energies.

Another method was to connect the telephonie apparatus to the transmission lines v at a sufficiently far distance from the central station, and in that manner compensate for the alterations ofV connection of the central station upon the knowledge and theory that the wave lengths of the conductors leading to the central station gave the necessary compensation. A, sufficient independence, however, cannot always be attained by this means, and on the other hand, such an arrangement of the telephonie apparatus causes considerable technical difficulties at great expense.

fn other instances both measures were employed if the alterations of connection vere not sufficiently compensated by the wave resistance of the above-mentioned conductors.

lt is obvious that all these prior usual means are only vincompetent and insufficient remedies.

The present invention overcomes this difficulty at its root by equalizing the possible state of the ends vof the transmission lines to one another with regard to the carrier frequency used. In other words, a uniform state of the ends of the lines is obtained.

y It has already been mentioned that the circuits of the central station or the switch station, represent a certain apparent impedance to the carrier frequency. The busbars are capacitively or inductively coupled to earth or to one another, and the transformers or voltage converters have an inductive or capacitive character with regard to the carrier frequency according to its size.

he result is a certain apparent impedance of the whole high tension system of a central station and in case high carrier frequency and earth return connections are employed, a switch plant mostly represents a comparatively very low capacitive impedance. There are two ways, different in principle, for equalizing the different conditions of the ends of the lines to one another. The character of the loading of the carrier frequency caused by the central station can be compensated by shun-ted apparatus of opposite phase, and in this manner cause the loading to correspond to a high ohmic resistance. If the transmission lines have been disconnected, the state of the ends of the lines with regard to the carrier frequency is practically unaltered.

An object of the invention is to provide means of the character above described which will be cheaper, safer and better than those heretofore in use.

@ther objects will be apparent from the following specification and claims when considered with the accompanying drawings.

The above referred to choke coils or blocking circuits, however, must be made of convenient cross-sectional area in order that the power working currents may not be caused to undergo undue voltage drops. Since in many cases currents of several hundred amperes are dealt with, and since further with a view of effective operation of Vthe choke coils or blocking circuits, the inductance values must not fall below certain minima, a number of difficulties are encountered in the practical performance of the idea. The choke coils or blocking eircuits would assume proportions that would prevent their convenient mounting and would necessitate special constructional It is well known that the inductance of a coil for definite frequencies can be considerably increased by coupling thereto a conveniently timed circuit. Now, the subjectmatter of this application relates to the use of this method in the present case, the extremely valuable advantage being thereby realizedv in practice that a small coil will prove adequate for mounting and connection in the different phases of the high tension power transmission lines. fn fact, this coil need consist only of a few turns 4and it is therefore an easy task to arrange the same in existent plants. Such phase coil, as it were, merely serves the object of conducting the working power current without an appreciable voltage drop being caused by it, while the circuit coupled thereto only has the purpose of increasing the inductanee to radio frequencies without it being necessary to choose a considerable wire section therefor.

In order that disturbances in the normal high tension power protection system may be avoided, the said phase choke coils can be rendered ineffective for overvoltage waves or surges, sometimes called transient phenomena, by means of a spark-gap which breaks down at very low voltages. In series with the spark gaps may be arranged ohmic resistances. The same method is recommendable also for the purpose of affording protection for the coupled circuit against damage by overvoltaoes.

In wire radio telephony along high tension power mains two wave lengths are generally used for multiplex telephony communication. lt is, as will be noted, then necessary to obtain separation of the communication air lines from the central station or switch houses simultaneously for both frequencies. This can be accomplished by using two series-connected phase choking devices according to the present invention. However, the second choking device may be dispensed with and saved if the first choking'device is given a two-wave characteristic. A number of forms of construction shall be indicated as follows:

(a) The problem can be solved by coupling two distinct and convenient tuned circuits to the one coil provided.

(b) Or else but one coil is used which is closed by a branch shunt. For one of the two frequencies utilized, one branch, in virtue of the series arrangement of a blocking circuit` constitutes a. verv high ohmic resistance, while the second one possesses the apparent resistance (impedance) required for the tuning, conditions being inversed with regard to the second frequency.

(c) Or else again the first coupled circuit can be further coupled through a small coil with an additional circuit which for the second carrier frequency just imparts the impedance to the first circuit in order to render it effective also for the second carrier wave.

The above invention will be more clearly understood when reference is madel to the accompanying drawings which form a part of my disclosure wherein:

Fig. l is a diagrammatic showingof one form of invention.

Fig. 2 discloses a system similar to Fig. l using a two wire system instead of a ground return.

Fig. 3 shows a single low impedance choke with two tuned circuits coupled thereto such as could be used with either Figures l or 2 instead of the means there shown.

Fig. 3a discloses a modification of Fig. 3 wherein the two tuned circuits are capacitively coupled to each other and inductively coupled to the line through one tuned circuit.

Fig. 4 discloses a further modification of Fig. 3 with a special blocking means for lower frequencies.

Fig. 4a is an arrangement similar to Fig. 4 with a special blocking means for higher frequencies and Fig. 5 is a still further modification in which coils tuned to separate frequencies are coupled to the transmission line through one of these coils.

Making reference to the drawings, a transmission liney l is connected to a source of energy 2 which may be either low frequency or even direct current if desired. Connected at a point in advance of the power source 2 is a source of high frequency energy l0 which source may, if desired, develop two separate and distinct frequencies f and f. Connected in the line l between the high frequency source l0 and the power or power source 2 are a plurality of phase coils 5 and 6 which coils provide a low impedance choke to the energy from the source 2. Inductively coupled with the coils 5 and 6 are the tuned circuits 3 and 4, circuit 3, for example, being tuned to frequency f and circuit 4 to frequency f. As before stated, these circuits when coupled to the chokes 5 and 6 provide a high impedance path with respect to the high frequencies but not with respect to the low power line frequency.

For the purpose of protecting the high tension power system from disturbances, the phase coils 5 and 6 may befprotected and rendered ineffective for over voltages or surges by means of spark gaps 8 and 9, respectively. These spark gaps are adapted to break down at very lowv voltages and in one of them a damping resistance 7 is inserted. .In this showing a ground return system and single transmission line is used. The ground is indicated at (l.

The modification shown in Fig. 2 is substantially the same as Fig. Yl wherein the 'tuned circuits 23, 24 correspond to tuned circuits 3 and 4 of Fig. 1 and the chokes or phase coils 25 and 26 correspond to the chokes or phase coils 5 and 6 respectively, also the spark gaps 28, 29 correspond to 3 and 9 of Fig. l. Since this system is designed for operation as a two wire system rather than the grounded return of Fig. 1 similarly tuned circuits to 23 and 24 are' supplied at 23 and 24. In this system the source of high tension power energy is indicated at 22 and the source of high frequency telephone energy at 20, and 2l, 2l are the two power lines.

ln Fig. 3the coils in circuits-31, 32 tuned respectively to the frequency f and f are coupled to a single choke or phase coil 5 which is similar to 5 of Fig. l, and due to tuning of circuits 31, 32 will provide a high impedance to both frequencies f and f.

Fig. 3a shows a further modification whereinV the tuned circuit 33 is coupled t0 the choke 5 and is tuned to a frequency f and the tuned circuit 34 which is tuned to frequency f is capacitively coupled to 5 through the circuit 33.

In Figs. 4 and 4a are shown further modifications of the system previously disclosed in which a special means for blocking either the higher or the lower frequency is connected in parallel with the choke 5 and a second circuit which is tuned to the other frequency either jl or f is inductively coupled with the choke 5', for example, the circuit 35 may be tuned to block out the lower frequency f and the circuit 36 tuned to the frequency f and inversely the circuit 38 will serve to block the higher frequency f from the source 2 and the tuned circuit 37 is tuned to the other frequency Fig. 5 shows an arrangement similar to Fig. 3a except that the circuitV 39 may be tuned to a frequency f and the inductively coupled circuit 40 is tuned to a higher frequency j and whencoupled through the circuit 39 to the choke 5 will block higher frequencies.

'Ihe operation of the arrangement may be briefly delined as follows:

The source 2 serves to supply high tension power on the line l and at the same time the source 10 will supply high frequency carrier currents for the telephonic communication and if desired carrier currents supplied by source l0 may be of two frequencies f and f so that multiplex communication may be established. It is well known that if the source 2 is removed from the line without any means for blocking the higher frequencies Vthat the same would be grounded through the switch which threw the generator off the line, since in most cases it is preferred to ground the transmission line upon cutting olf the power supply, and, therefore, the telephonie communication would be rendered ineffective. Also it is most inconvenient and unpracticable to supply the usual form of choke coil for blocking these high frequencies due to the unwarranted size and since a high impedance may be developed in a smaller coil by inductively connecting a tuned circuit thereto the equivalent of a high impedance choke is realized` 'by coupling circuits, as for example, 3, 4,

tuned to frequencies f, f to coils 5 and 6. The high impedance choke 5, therefore, will serve to protect the apparatus 2 from high frequency f and at the same time prevent this frequency from being grounded upon the source 2 being removed from the line and form a means of protecting workmen who may be repairing the generator apparatus. Likewise the high impedance 6 will serve to block the other frequency 7" which is generated in the source of high frequency l0 and protect the apparatus and workmen in a similar manner to the high impedance used from excessively high frequencies, as

well as to prevent interruption of telephonie communications by blocking out any high frequencies which might otherwise pass through the utilized apparatus and into the ground.

The operation above described is equally applicable to Fig. 2 other than the fact that the wire 21 will serve the same purpose as the ground G of Fig. l. In the arrangements shown in the Figures 3 to 5 inclusive, it is often convenient to eliminate one of the chokes 5 or 6 and supply instead two circuits which are tuned to the frequency f and f which will, when coupled with the choke 5 indicated in all these figures, serve the same purpose as the tuned circuit 3 coupled to the choke 5 and the tuned circuit 4 coupled to the choke 6.

Having described my invention, I claim:

l. Means for insuring continuous service in wired radio frequency telephony on high tension lines regardless of conditions at ends of said lines comprising a source of high tension energy, a source of high frequency telephony energy adapted to generate a plurality of carrier frequencies, and means connected between said high tension source and said high frequency source for blocking the high frequency energy from said high tension source said blocking means comprising an inductance and a tuned circuit coupled thereto, said circuit being tuned to one separate carrier frequency and another tuned circuit coupled to said first mentioned tuned circuit and being tuned to another of said carrier frequencies whereby a path, of high impedance to each high frequency and a path of low impedance to said high tension energy is provided.

2. Means for insuring continuous service in wired radio frequency telephony on high tension lines regardless of conditions kat the ends of said lines comprising a source of high tension energy, a source ofhigh frequency telephony energy adapted to generate a plurality of carrier frequencies and means between said high tension source and said high frequency source for blocking the high frequency energy from said high tension source, said blocking means comprising an inductance, a plurality of tuned circuits coupled to each other, one Vthereof being coupled to said inductance, each of said tuned circuits being tuned to a separate one of said plurality of said carrier frequencies whereby a path of high impedance to each high frequency and a path of low impedance to said high tension energy is provided.

3. Means for insuring continuous service in wired radio frequency telephony on high tension lines regardless of conditions at ends of said lines comprising a source of high tension energy, a source of high frequency telephony energy adapted to generate a plurality of carrier frequencies, and means connected between said high tension source and said high frequency source for blocking the high frequency energy from said high tension source said blocking means comprising an inductance and a tuned circuit coupled thereto, said circuit being tuned to one separate carrier frequency and another tuned circuit capacitively coupled to said first mentioned tuned circuit and being tuned to another of said carrier frequencies whereby a path of high impedance to each high frequency and a path of low impedance to said high tension energy is provided.

4. Means for insuring continuous service in wired radio frequency telephony on high tension lines regardless of conditions at the ends of said lines comprising a source of high tension energy, a source of high frequency telephony energy adapted to generate a plurality of carrier frequencies and means between said high tension source and said high frequency source for blocking the high frequency energy from said high tension source, said blocking means comprising an inductance, a plurality of tuned circuits capacitively coupled to each other, one thereof being coupled to said inductance, each of said tuned circuits being tuned to a separate one of said plurality of said carrier frequencies whereby a path of high impedance to each high frequency and a path of low impedance to said high tension energy is provided.

PAUL TATZ. 

